Generally speaking, when it comes to a method to decorate molded products such as automobile parts and electrical appliances, a technique designed to decorate decorable objects by spray-coating multiple layers with different functions such as an adhesive layer, color layer and protective layer one by one to confer durability, esthetic design and the like on them has been adopted. However, there is a problem with such a technique in that, since spray-coating necessitates a baking step, there are more steps than otherwise is the case, the cost is high due to the considerable energy and time involved in heating. To solve this problem, film-based decorating methods capable of decorating three-dimensional decorable objects, such as vacuum molding and air-pressure forming, have been studied in recent years.
Designed to cover the outermost surface of a molded product, the protective layer of a multilayer film for decorative molding used in a film-based decorating method plays an important role in the decoration of a molded product, and, as such, needs to possess durability (for instance, anti-scratching properties (scratch resistance), weather resistance, chemical resistance and water resistance).
In addition, when applying a film-based decorating method to automobile and other parts, mold-conformability during decorative molding is essential because of the large size and complex shape of molded products. Namely, to decorate a molded product using a film-based decorating method, it is necessary that the whole surface from top to bottom be covered in one go even if the molded product is large in size. Similarly, when a complex shape is involved, the multilayer film for decorative molding needs to fit the whole surface by deforming to the shape of every peak and trough.
The protective layer of a multilayer film for decorative molding needs particularly to have scratch resistance and, as part of a multilayer film for decorative molding, mold-conformability during decorative molding, and there are growing calls for those characteristics.
Further, application of a film-based decorating method to automobile and other parts is accompanied by a requirement for high productivity, namely the completion of a molding operation with only a few steps.
As a multilayer film for decorative molding, a moldable film featuring a protective layer that mainly comprises an acrylic resin as described in Japanese Unexamined Patent Publication (Kokai) No. 2004-299223, Official Gazette and Japanese Unexamined Patent Publication (Kokai) No. 2003-212938, Official Gazette, for instance, has been proposed.
A moldable film that mainly comprises urethane resin and is designed to be cured by heat curing alone as described in Japanese Unexamined Patent Publication (Kokai) No. 2010-260942, Official Gazette has also been proposed.
The method described in Japanese Unexamined Patent Publication (Kokai) No. 2004-299223, Official Gazette and Japanese Unexamined Patent Publication (Kokai) No. 2003-212938, Official Gazette has a problem in that its productivity is low because it needs to, after bonding a multilayer film for decorative molding to the decorable object, run an extra step of irradiating it with an energy ray using a UV lamp to cure the protective layer. The method described in Japanese Unexamined Patent Publication (Kokai) No. 2010-260942, Official Gazette also has a problem in that it cannot simultaneously achieve the scratch resistance of the protective layer and its mold-conformability during decorative molding despite both being essential properties.
In light of such limitations, it could be helpful to provide a high-productivity multilayer film for decorative molding that features a protective layer having both good stretchability, as suited for film-based decorative molding, and good scratch resistance.